A comprehensive study on improved power materials for high-temperature thermoelectric generators

Abstract Dense Ca 3 Co 4 O 9 -Na x CoO 2 -Bi 2 Ca 2 Co 2 O 9 (CCO-NCO-BCCO) nanocomposites were produced from sol-gel derived Ca 2.25 Na 0.3 Bi 0.35 Tb 0.1 Co 4 O 9 powder by four methods: Hot-pressing (HP), spark plasma sintering (SPS) and pressureless sintering in air or O 2 atmosphere. Nanocomposites from HP and SPS revealed nanosized grains and showed a thermoelectric power factor of 4.8 and 6.6  μ W ⋅ cm −1 ⋅ K −2 , respectively, at 1073 K in air. A dense 2D nanocomposite with structures on multiple length scales and enhanced thermoelectric properties was obtained from pressureless sintering in O 2 atmosphere. The resulting 2D nanocomposite enabled the simultaneous increase in isothermal electrical conductivity σ and Seebeck coefficient α , and showed a thermoelectric power factor of 8.2  μ W ⋅ cm −1 ⋅ K −2 at 1073 K in air. The impact of materials with enhanced electrical conductivity and power factor on the electrical power output of thermoelectric generators was verified in prototypes. A high electrical power output and power density of 22.7 mW and 113.5 mW ⋅ cm −2 , respectively, were obtained, when a hot-side temperature of 1073 K and a temperature difference of 251 K were applied. Different p- and n-type materials were used to verify the effect of the thermoelectric figure-of-merit z T and power factor on the performance of thermoelectric generators.